Method of making a lined conduit section

ABSTRACT

A curved section is provided for connecting in a conduit through which passes a fluid stream having solid material entrained therein. A plurality of wear strips are attached to the inside wall of the curved section. They are positioned for the solid material to impinge thereon as the fluid stream changes its direction of flow as it passes through the curved section. The wear strips are elongated members of wear resistant material positioned side-by-side along the inside wall against which the solid material impinges. The abutting sides of adjacent wear strips are beveled so that the outer edges of one adjacent strip extends over the inner edge of the other adjacent strip to provide a continuous surface of wear resistant material in the path of the entrained solid material. The wear strips are attached to the side wall of the curved section by bodies of weld metal located in openings in the wear strips that are smaller in cross-sectional area adjacent the wall to which the members are attached than they are on their outside exposed surfaces and the weld metal is applied by sequentially puddling small amounts of weld metal in first one than another of the openings so that the wear strips are not raised to a temperature that would cause the cracking of the hard wear material due to thermal stress.

This is a continuation-in-part of Ser. No. 850,285, filed Nov. 10, 1977,and entitled "Lined Flat Back", now abandoned.

This invention relates to curved sections of conduits that are linedwith wear resistant material to resist the erosive effect of solidmaterial entrained in the fluid stream passing through the conduit.

It is common practice to transport solid particulate material byentraining the material in a fluid stream as it moves through a conduit.For example, in the operation of pulp mills, wood chips, sawdust and thelike are moved to the desired location by entraining the particles in anair stream that is forced through a conduit. Unfortunately, suchconduits very rarely travel in a straight line so there will be one ormore sections in the conduit where the solid material will impingeagainst a side wall of the conduit as the fluid stream changesdirection. As these solid particles impinge against the side wall ofsuch sections, they will erode away the side wall requiring frequentreplacement of these sections in the conduit. This has been along-standing and well-recognized maintenance problem and much efforthas been made to increase the life of these curved sections in this typeof conduit.

It is an object of this invention to provide an improved curved sectionfor connecting in a conduit of this type that is lined withwear-resistant material in the form of a plurality of side-by-sidestrips of the material that provide a continuous surface ofwear-resistant material in position to receive the impact of the solidmaterial carried by the fluid stream in the conduit.

It is a further object of this invention to provide such a curvedsection that is lined with a plurality of generally, rectangularlyshaped elongated wear strips having their adjacent sides beveled so thatone edge of one adjacent wear strip overlaps the edge of the adjacentstrip to provide a continuous wear-resistant surface for receiving theimpact of the solid material and which allows flat-sided wear strips ofwear-resistant material that can be easily cast to be readily attachedto the inside wall of a section of conduit even though the wall curves.

It is a further object of this invention to provide a wear strip ormember of high abrasive material that is shaped so that a plurality ofsuch members can be easily positioned in conduits that are circular orrectanular in cross section to provide a continuous abrasive-resistantsurface to receive the impact of the solid material moving through theconduit.

It is a further object of this invention to provide a method of liningan inside surface of a conduit by which individual wear strips areattached to the inside surface of the conduit using a welding methodthat keeps the individual wear strips at a temperature below thetemperature that will cause the strips to crack due to thermal stressand, yet will securely attach the strips in the desired position on theinside surface of a conduit.

These and other objects, advantages, and features of this invention willbe apparent to those skilled in the art from a consideration of thisspecification, including the attached drawings and appended claims.

IN THE DRAWINGS

FIG. 1 is a side view partly in elevation and partly in section, of acurved section of conduit that is rectangular in cross-section and thatis lined in accordance with this invention with a plurality of wearstrips.

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1.

FIG. 3 is a sectional view taken along line 3--3 of FIG. 2.

FIG. 4 is a sectional view of an enlarged scale taken along line 4--4 ofFIG. 3.

FIG. 5 is a sectional view taken along line 5--5 of FIG. 4.

FIG. 6 is a curved section of a conduit that is tubular in cross sectionand that is provided with the wear strip in accordance with thisinvention.

FIG. 7 is a sectional view taken along line 7--7 of FIG. 6.

FIG. 8 is a cross-sectional view of an enlarged scale showing therelationship of the flat-sided wear strip relative to each other and tothe curved side wall of the conduit.

FIGS. 1 through 5 show the invention of this application as applied to acurved section of conduit that is rectangular in cross-section. This iscommonly referred to as a "lined flatback". This type section isso-called because the side wall against which the solid materialimpinges, i.e., the "wall, is flat in the transverse direction. Forexample, as shown in the drawings, conduit section 10 includes flatbacksidewall 12 that is positioned so that any solid material carried by thefluid stream passing through this section of the conduit will impingeagainst this back wall as it is forced to change direction. Theremainder of the conduit is made up of walls 14, 16, and 18 that areintegrally connected together in this embodiment. Walls 14 and 18 areprovided with longitudinally extending flanges 20 and 22 to which backwall 12 is attached by bolts 24. This allows the wall of the conduitthat is subjected to the most severe abrasion to be easily removed andrepaired or replaced, as required, without having to disconnect thesection from its position in the conduit.

In accordance with this invention, the side wall of the conduit thatreceives the impact of the solid material as it moves through inlet 25to outlet 26 is lined by a plurality of wear strips 28 that arepositioned in side-by-side relationship and that are made of a hardmaterial to provide a wear-resistant surface against which the solidmaterial will impinge as it moves through the section of conduit.

In this embodiment, the wear members extend along a line transverse thelongitudinal axis of the section. Several of the wear members are shownon an enlarged scale in FIG. 3. They extend between side wall 14 and 18of the conduit, as shown, the wall 12 to which it is attached ispositioned as shown in FIGS. 1 and 2. The flatback, or side 12, is flatin a transverse direction and curves in a longitudinal directionparallel to the radius of curvature of the section to which it isattached. Wear members 28 are elongated members that can be cast of wearresistant material without any pre-selected curvature and then arrangedside-by-side along the curved back side of the conduit to provide acontinuous wear resistant surface in the path of the particles carriedthrough the conduit. This greatly simplifies the manufacture of the wearstrips and allows the wear members to be used for different angles ofcurvature without being specially cast with a pre-selected shape.

This is accomplished in accordance with one feature of this invention bybeveling the adjacent edges of the wear members as shown in FIG. 4. Theangle of the bevel is selected so that edge 30 of wear strip 28a isoverlapped by the outer edge 32 of wear strip 28b when the two arepositioned as shown in FIG. 4. In this way, flat wear strips can bepositioned side-by-side along a curved surface to provide a continuousprotective cover for the underlying wall of the conduit. If the sideswere straight only the outer edges could touch and any shifting of thestrips would produce a gap between them.

The wear members, as stated above, are cast of extremely hard materialso that they will resist erosion by the impingement of the solidmaterial. One such material, for example, is tungsten carbide. Anotheris an alloy having a high chromium content. For examply, in onepreferred alloy the chromium content is 27% with 3% carbon. Thismaterial being extremely hard is also very brittle and when subjected touneven heating will tend to crack. Therefore, it is one of the featuresof this invention to provide a method for attached wear strips to theside wall of a section of conduit in a manner to avoid undue thermalstressing of the very hard and brittle material from which the wearstrips are made.

In accordance with this feature of the invention, each wear strip iscast with a plurality of openings 34 spaced along its length, as shownin FIG. 3. These openings are smaller in cross section one one end thanon the other. In other words, the walls of the opening taper so as toconverge toward the side of the wear strip that is going to be attachedto the inside wall of the conduit. Thus, the cross-sectional area of theopenings adjacent side wall 12, as shown in FIGS. 4 and 5, is smaller incross section than the section of the opening adjacent the outer surfaceof the wear members. This allows the opening to be filled with weldmetal, indicated by the number 36, that does not have to fuse to thewear strips themselves in order to hold them in place. All that isrequired is that fusion occur between the relatively soft, usuallylow-carbon steel material that makes up the side wall of the conduit anddue to the shape of the opening in 34 in which the weld metal is locatedwill securely attach the wear members to the side walls.

It has been discovered, however, that to fill an opening 34 with weldmetal in one operation will invariably raise the temperature of the wearstrip adjacent the opening sufficiently to produce thermal stresses thatwill crack the strip. In other words, the strips are so hard and brittlethat they cannot be welded to the back wall in the conventional manner.

In accordance with the method of this invention, the welder will line upthe strips in the desired position on the surface of the conduit to belined. The surface has to be generally flat, at least at the openingreceiving weld metal. The welder than puddles a small amount of weldmetal in one of the openings. Opening 34a in FIG. 3 for example. Hecarefully watches the material around the opening and by observation orby using a temperature stick stops puddling weld metal in the openingbefore the temperature around the opening approaches that when the stripmay crack. He then moves to another, preferably remote, opening, such as34b, 34d, or 34e and repeats the puddling operation. He may them move to34c, etc, but eventually he will return to 34a, which has now cooled offand puddle more weld metal in the opening. This procedure is repeateduntil all of the openings are filled with weld metal.

The weld metal is not fused to the wear strips, but only to the sidewall of the conduit. It has been discovered, however, that the puddledweld metal will draw carbon out of the wear strips in substantialamounts, which raises the hardness of the weld metal substantially. Thehardness of the weld metal, in fact, is such that it resists erosion bythe particulate matter flowing through the conduit almost assuccessfully as the wear material itself.

In FIGS. 6 through 9, the invention is shown applied to a tubularconduit, that is one that is circular in cross section. The curvedsection of conduit that is lined with the wear members of this inventionis shown in FIG. 6 as being made up of a plurality of individual,generally straight sections 40 through 45. The end of each section iscut at an angle to its longitudinal axis and then the sections areconnected together in a conventional manner by flanges 46 (the bolts arenot shown) to form the curved section of the conduit. In thisembodiment, each of sections 40 through 45 has the side wall againstwhich the material will impinge covered by a plurality of wear strips 48that extend parallel to the longitudinal axis of the sections to whichthey're attached. In other words, in this embodiment, the side walls towhich the wear members are attached are generally straight or flat inthe longitudinal direction and are curved in the transverse direction.Here again, by providing wear members with beveled sides they can becast as flat members that are elongated in one direction and generallyrectangular in cross section, the casting procedure is greatlysimplified, as explained above. The overlapping bevelled edges functionin the same manner as described above and as shown in FIGS. 4, 5, and 8.

These wear members are attached to the inside wall of the sections ofconduit in the same manner as described above by welds 50 that arepositioned in openings shaped in the same manner as shown in FIGS. 4 and5.

As the generally flat-sides wear members are positioned adjacent to eachother against the curved inside wall of the section, such as wall 51 orsection 42, the outer edges of the adjacent members will contact andthen the sides will diverge in the directon of the side wall. This voidbetween the members may be filled with an epoxy resin containingparticles of steel. In this way, should the overlapping adjacent edgesof the wear members erode away, the relatively soft side wall of theconduit will be protected from direct impingement by the particlesmoving through the conduit by this mass of epoxy reinforced with thesteel particles.

From the foregoing it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forth,together with other advantages which are obvious and which are inherentto the apparatus.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

The invention having been described what is claimed is:
 1. A method oflining an inside surface of a conduit with a plurality of strips ofhard, relatively brittle, wear resistant material formed into elongatedrelatively narrow strips that have openings therethrough that havesmaller cross-sectional areas on one side than on the other said methodcomprising the steps of disposing the inside surface in a generallyupwardly facing horizontal position, placing a plurality of the stripson the upwardly facing surface in adjacent side-by-side position withthe ends of the openings in the strips with the smaller cross-sectionalarea adjacent the upwardly facing surface, puddling weld metal brieflyin first one opening and then another remote from the first whileallowing the weld metal in said first opening to cool, briefly puddlingadditional weld metal in said first one opening, likewise puddling weldmetal in each said opening at plural brief intervals until each openingis filled to thereby maintain the temperature of the strips below thatat which they will crack due to thermal stresses. .Iadd.
 2. A method ofattaching to a surface of a conduit a strip of hard, relatively brittle,wear resistant material that has openings therethrough that have smallercross-sectional areas on one side than on the other, said methodcomprising the steps of disposing the surface in a generally upwardlyfacing horizontal position, placing the strip on the upwardly facingsurface with the ends of the openings in the strip with the smallercross-sectional area adjacent the upwardly facing surface, puddling weldmetal briefly in first one opening and then another remote from thefirst while allowing the weld metal in said first opening to cool,briefly puddling additional weld metal in said first one opening,likewise puddling weld metal in each said opening at plural briefintervals until each opening is filled to thereby maintain thetemperature of the strip below that at which it will crack due tothermal stresses. .Iaddend.